1. Field of the Invention
The present invention relates to a recording medium suitable for use in an ink-jet recording process, and a recording process employing the same. More particularly, it is concerned with a recording medium excellent in the ink receptivity, non-beading property, sharpness of recorded images and water resistance, and with an ink-jet recording process employing the same.
2. Related Background Art
In ink jet recording processes, the recording is carried out by forming ink droplets according to various ink (or recording liquid) ejection methods, for example, an electrostatic attraction method, a method in which mechanical vibration or displacement is applied to ink by use of a piezoelectric element, a method in which the pressure generated by heating ink and forcing it to foamis utilized, and so forth; and flying the droplets so that a part or the whole of them is adhered on a recording medium such as paper. These have been noted as recording processes that can be substantially free from noise and can perform high-speed printing and multi-color printing.
As the ink for ink-jet recording, those chiefly comprised of water are used in view of safety and recording performance, and polyhydric alcohols are often added thereto to prevent nozzles from being clogged and to improve the ejection stability.
As recording mediums used in the ink-jet recording process, therre have been hitherto used those comprising a porous ink-receiving layer provided on ordinary paper or on a substrate called ink-jet recording paper. However, with improved performances (such as increasing high-speed or multi-color recording) and widespread use of ink-jet recording devices, properties of a higher grade and wider range have been increasingly required also with respect to the recording mediums.
Namely, it is necessary for a recording medium used in ink-jet recording to obtain recorded images having a high resolution and high quality, to satisfy fundamental requirements that;
(1) ink is received by the recording medium as quickly as possible; PA1 (2) even when ink dots have been overlapped, the ink adhered later may not flow into the dots adhered earlier; PA1 (3) ink droplets may not diffuse over the recording medium to excessively enlarge the size of ink dots; PA1 (4) the shape of an ink dot is substantially round with smooth peripheries; PA1 (5) the ink dots have a high OD (optical density), and are free from unclearness around the dots; etc. PA1 (6) Coloring components of ink have a good color-forming property; PA1 (7) the recording medium has a particularly good ink fixation since the same number of droplets as the number of the colors of ink may sometimes adhere overlappingly at the same portion; PA1 (8) the surface is glossy; PA1 (9) it has a high whiteness; etc.
In addition to the performances required as above, the following performances are further required when recorded images having a high resolution comparable top color photographs are to be obtained by a multi-color ink-jet recording process:
The recorded images formed by the ink-jet recording process have been hitherto used solely for the surface image observation, but, with improved performance and widespread use of ink-jet recording devices, recording mediums suitable for use other than the surface image observation are being sought after.
The use other than the surface image observation may include a use in which images formed by projecting recorded images on a screen or the like by means of optical equipments such as a slide and an OHP (over head projector) are observed, a use as a color separation plate used when producing a positive plate for color printing, a use as a CMF (color mosaic filter) used for color display by liquid crystals, etc.
While diffused light of recorded images is principally observed when a recording medium is used for the surface image observation, what becomes a problem in the recording medium for the above uses is the transmitted light of the recorded images. Thus, in addition to the performances required as above in the recording medium for the ordinary ink-jet recording, the recording medium is further required to be excellent and in the light transmission properties, in particular, linear transmittance.
However, in the present state of the art, no recording medium that has satisfied all of these required performances has been available.
Moreover, many of the conventional recording mediums for the surface image observation have been employed in a system in which a porous ink-receiving layer is provided on its surface and ink is received in porous voids in the layer to fix a recording agent. Accordingly, because of the porousness, there has been no gloss on the surface of the recording mediums.
On the other hand, when the ink-receiving layer has a non-porous surface, there have been the disadvantages that non-volatile components in the ink, such as polyhydric alcohols, may remain unremoved from the surface of the recording medium for a long time after recording to prolong the time required for the ink to be dried and fixed, whereby clothes may be soiled when touched to the recorded images or the recorded images may be damaged.
There have been also the disadvantages that when the ink droplets are adhered on the ink-receiving layer, the ink droplets may irregularly migrate to cause image density unevenness called "beading", and the ink may be mutually mixed at the boundary portions at which ink droplets of different colors are adhered, resulting in irregularities of images and no sharp image obtained. Particularly when high density and high speed printing is carried out, the ink may increase in quantity to make these disadvantages more remarkable.
In the instance of the recording medium in which a water-soluble polymer is used for the formation of the ink-receiving layer in order to enhance the affinity for ink and the ink receptivity, there also can be the problem that the surface of this ink-receiving layer may become viscous under the condition of a high humidity, so that it may adhere to a lead-on roll of a printer when set in the printer, and that the recording medium can not be carried or the recording medium may suffer blocking when laid overlappingly.